Such illumination systems are known per se. They are used, inter alia, in luminaires for general lighting purposes, for example, for office lights, for shop lights or, for example, for shop window lights. Alternatively these illumination system are used for lighting of (transparent or semi-transparent) plates of glass or of (transparent) plates of glass or of (transparent) synthetic resin on which items, for example jewelry, are displayed. Further alternatively the illumination system is used for illuminating advertising boards, for example, advertising boards illuminating a partially transparent image from the back of the image.
The known illumination systems may also be used as light sources in backlighting systems in (picture) display devices, for example, for TV sets and monitors. Such illumination systems are particularly suitable for use as backlighting systems for non-emissive displays such as liquid crystal display devices, also denoted LCD panels, which are used in (portable) computers or (portable) telephones.
Illumination system comprising a light source having a substantially Lambertian emission profile, for example, light emitting diodes (further also referred to as LEDs) are recently more frequently used in general lighting applications, such as luminaires. The benefit when using LEDs in luminaires is that the efficiency of the LEDs is relatively high. Furthermore, the range of available LEDs for use in general light applications is vast offering excellent design freedom in respect to emitted color and aesthetic design of the luminaire. A drawback of the use of LEDs is that the light emitting surface typically is relatively small and the intensity of light emitted from this relatively small surface is high. The shielding of this light emitting surface to a user of the luminaire is important to prevent glare. Glare results from excessive contrast between bright and dark areas in the field of view. Glare can, for example, result from directly viewing a filament of an unshielded or badly shielded light source. Especially when using LEDs, direct view into the LEDs by a user near the luminaire should be prevented to reduce the glare of the luminaire and increases the visual comfort of the user. A luminaire comprising LEDs as a light source is, for example, known from WO 2007/054889. In this luminaire the light emitted by the LEDs is emitted via a back-reflector to reduce the glare and improve the uniformity of the light emitted from the luminaire. A disadvantage of the known luminaire is that the height is relatively large.